1. Field of the Invention
The present invention relates to ceramic substrates for tip electronic parts such as tip resistors, tip capacitors, and so on, and particularly relates to a ceramic substrate for electronic parts in which numbers of electrodes, resistors, and the like, are formed on the substrate by printing and then the substrate is divided into pieces to obtain numbers of tip parts.
2. Description of the Prior Art
Referring to FIGS. 6 through 8, description will be made hereunder as to a structure of a conventional tip resistor and the method of manufacturing the same.
First, a slurry made by mixing ceramic powder, binder resin, etc., is molded into a thin plate-like green sheet. Grooves 2 and 3 are formed in the green sheet by press-molding. The grooves 2 and 3 are respectively arranged longitudinally and transversely at predetermined intervals as shown in the drawings so that the grooves can be used as split grooves to divide the substrate into individual tip resistors later. Next, the green sheet is baked to obtain a hard ceramic substrate 1, electrodes 4 are formed by screen printing on the ceramic substrate 1 so as to be laid over each of the grooves 2, resistors 5 are formed by printing between the adjacent electrodes 4 as shown in the drawings, an overcoat 6 of a glass material is applied over the resistors 5, the ceramic substrate 1 is baked, and then the ceramic substrate 1 is divided along the grooves 2 so as to obtain a plurality of elongated ceramic subdivisions 1a each having a train of numbers of resistors formed thereon as shown in FIG. 8. Then, side electrodes 7 and back electrodes 8 are formed at the side and back surfaces of each of the ceramic subdivisions 1a by printing so as to be connected to the electrodes 4 as shown in FIG. 7. Thereafter, each of the ceramic subdivisions 1a is divided along the other split grooves 3 of the ceramic split plate 1a, and the electrodes 4, 7, and 8 are nickel-plated and further solder-plated to thereby obtain a number of individual tip resistors A.
However, the tip resistors are individually separated by snapping the substrate along the grooves 2 and 3 formed in the substrate and therefore burrs may be easily formed at the dividing surface portions so as to make it excessively difficult to form external electrodes (side electrodes 7) which are formed after the division of the substrate.
Further, when the electrodes 4 and the resistors 5 are formed by printing on the tip resistors, it is necessary to fix the ceramic substrate 1 on a fixing board 17 and to put a mask in position thereon.
FIGS. 9, 10, and 11 are views for explaining the positioning in printing work. First, as shown in FIG. 9, two reference surfaces 17a perpendicular to each other are formed on the fixing board 17 and two sides of the ceramic substrate 1 perpendicular to each other are urged against the reference surfaces 17a by movable pins 17b so that the ceramic substrate 1 is fixed. Next, a mask 20 shaped into a predetermined pattern is put on the ceramic substrate 1 and electrodes or resistors are formed on the ceramic substrate 1 by screen-printing. In the above-mentioned printing method, however, the positioning of the mask 20 on the ceramic substrate 1 is generally performed by eye-measurement for the two sides of the ceramic substrate 1 perpendicular to each other. Assuming that a dimensional error of a special mask 20 with respect to a specific ceramic substrate 1 at two sides thereof perpendicular to each other is zero, a displacement between the specific mask 20 and the specific ceramic substrate 1 at the two sides opposite to the first-mentioned two sides is also zero. However, if a dimensional error of another ceramic substrate at two sides perpendicular to each other is a, a displacement between the above-mentioned mask 20 and the other substrate at the two sides of the substrate opposite to the first-mentioned two sides is also a. Furthermore, it is generally difficult to strictly control the dimensional accuracy of the ceramic substrate, so that the above-mentioned displacement a cannot be neglected if, for example, the fact that the shrinkage rate in baking reaches about 20 percent is taken into consideration.
Accordingly, such a method has been widely employed in which ceramic substrates 1 are classified in advance into several groups in accordance with the size of the ceramic substrates 1 and masks having specific dimensions corresponding to the respective groups are prepared, so that in printing a specific mask is selected from the prepared masks correspondingly to a specific substrate on which printing is performed to thereby minimize the error a.
Such handling, however, unnecessarily increases the kind of the masks and excessively lowers the work efficiency.